Head circumference size 54-63cm, Product Name City cycling helmet, Product weight 493g, Shell material ABS, Product size 28X22X16cm (average size), Cushioning layer material EPP, Model NXG-2020M-XK, Goggle material PC.
Basically copy coupon, view price history or create e-mail price alert. What is best price?
Aliexpress
There’re some similar (or not) items on Aliexpress
You can use link bot to get even lower price:
Click here to search by yourself. Here are coupons that you can use.
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
1. ($44.99): BG59dcd1
2. ($64.10): Cuponation9
3. ($64.80): BG8ReviTrage
4. ($66.21): BG00c906
put item in your cart and apply coupon code there after clicking “Proceed to checkout”. Click to copy code and open shop.
Additional Banggood coupons: first page and second page
Old coupons (from the oldest to the newest): BGMUA7, BGAFF10OFF, BGMUA8, BGCuponation10, BGTY503DL, BGC202G, BG10OFFAFF, BGwhielabel, 13f142, BG10OFFAFF1, BG4d9120, 00c906, ADMITAD2212, 2022ACTIESNL, Terence, Tabby20, 2203ActiesNL, BG1efeb0, 8Couponsde, MVC8SPRING, 8BGwbg2204, BG8e3c92, tRaDetRaCKeR, 8wEbgaInS5, pROMo8cuPoN, BG71c041, hoNEYbGdeAlS, BGd8c503
(sometimes old coupons work, so you can check them out (this site checks them on every price update))
Price history and price alert
Price history (for all/most countries) for Xiaomi Niuxiaoge CityCycling Helmet is here. The lowest price was: $34.99.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood and Aliexpress (only if product name will be the same as on Banggood and I will post it on social media though, so it’s more like Banggood price alert)).